ORLANDO, Fla., Jan. 21 (UPI) -- When three new Mars missions reach the Red Planet in February, recording the first sounds from another planet is to be among the scientific milestones.
NASA expects its Perseverance rover to land Feb. 18, after the United Arab Emirates' Hope orbiter arrives Feb. 9 and China's Tianwen-1 mission arrives the next day.
Perseverance carries two microphones. One will record the noise made by laser pulses emitted from the rover to hit rocks, which will help scientists identify their types.
The other microphone will record the sound of the spacecraft entering the Mars atmosphere and anything else it can "hear" on the surface.
Those sounds may be muted by the thin Martian atmosphere, so NASA recently posted a demonstration online of familiar Earth sounds and what they might be like on Mars.
"Some sounds that we're used to on Earth, like whistles, bells or bird songs, would almost be inaudible on Mars," NASA said in an article accompanied by a list of recordings.
NASA's recordings include the sound of high-pitched birds chirping on Earth, next to a recording of what that would sound like on Mars -- near silence.
That's because the atmosphere on Mars is only about 1% as thick as Earth's, and is mostly carbon dioxide -- so sound waves behave differently there.
Sound will be different because the density, temperature and composition of the Mars atmosphere is greatly different than Earth's, said James Nabity, associate professor in aerospace engineering at Colorado University at Boulder.
"I expect sounds to have longer wavelengths, lower frequency, on Mars ... due to a carbon dioxide-dominant atmosphere," Nabity said in an email. "Imagine the effect of helium on the human voice versus same in a standard atmosphere; only now it's reversed."
Such effects of carbon dioxide could lower the frequency of the human voice by one-third, according to NASA.
Since Mars appears to be a sterile, cold world, the rover would be limited in what sounds it could pick up from the environment, Nabity said.
"I expect we'd hear wind, falling boulders, shifting surfaces or Marsquakes" and possibly meteors if the rover is in the right place at the right time, he said.
Most of the sounds recorded by Perseverance will come from the rover itself, said Ken Williford, deputy project scientist for the NASA Mars 2020 mission at NASA's Jet Propulsion Laboratory in California.
"Wind is the obvious one. We have regular winds, but also dust devils that could be carrying sand and that could make a lot of noise," Williford said. "Other rover noises could be dramatic, such as the wheels crunching over Mars dust and rocks, or the sound of drilling into rock."
The sounds will be transmitted digitally from Mars and decoded much like sound files are downloaded on a home computer.
In a shared global clearinghouse of such data from space, JPL had to build a new category for sound data from another planet.
"Some people think the seismic waves we have measured with a seismometer on the Mars Insight Lander, but that is not technically sound, so this will be a first," Williford said.
Astronauts someday could talk to each other on Mars without using an intercom system, he said, as long as spacesuits didn't interfere.